Clnssification of the Crustacea. 453 



that tlie Phyllopod eye is overgrown by a reduplicature of the 

 skin, T interpreted the capsule of the eye of Argidus, which 

 was observed by Jurine * and Claus, as being of siniihar 

 origin f. Subsequent investigations of mine, conducted it is 

 true upon insufficient material, have, however, suggested to 

 me the possibility that in the case of Argiclus we may have to 

 deal with a modification of the condition which is found in 

 Estherida?, Cladocera, and Apus. According to the figures 

 which lie before me it would be possible that the eye simply 

 separates from the integument and descends into the subjacent 

 tissue. Nevertheless this does not exclude us from bringing 

 both modes of formation into relation one with another and 

 regarding them as modifications of essentially one and the 

 same process. I consider the sinking-in and roofing-over of 

 the compound lateral eyes of Argulus as an heirloom from the 

 Apodidje. 



It is also possible to institute a comparison between the 

 shape of the thoracic feet of Argulus and the special develop- 

 ment exhibited by the foot of Apus. In Argulus the four 

 pairs of thoracic feet are natatory appendages, and they each 

 consist of a two-jointed axial portion and two narrow rami 

 with many joint-like divisions, so that the entire limb reminds 

 us of that of the Cirripedes. When brought into comparison 

 with the swimming-feet of the existing Euphyllopods the 

 ioot of Argulus — and the larval conditions must not be left 

 out of consideration — with its elongated stem and the likewise 

 elongated slender rami, proves to resemble most the limb of 

 Apus in shape. Herein I have in my mind the common 

 general character of the two forms of limbs rather than an 

 agreement which goes into details. With reference to the 

 other points of agreement, that last alluded to appears to me 

 to be no mere casual one, but to be based upon the close 

 affinity between the two forms. Whether the flagellum 

 which occurs on both the anterior pairs of feet in Argulus 

 does not correspond to an epipodial appendage, and conse- 

 quently is likewise to be regarded as an heirloom from 

 ancestors resembling the Euphyllopods, I would not here 

 attempt to decide ; Claus compares it with the lancet-shaped 

 branchial appendage of the Cirripede limb. 



No connecting-points for phylogenetic investigations can be 

 gained from the formation of the mouth-parts of Argulus, 

 since in consequence of the parasitic mode of nutrition these 

 appendages have been greatly modified. On the other hand, 



* L. Jurine, " Memoire sur VArguh foliace,'^ Ann. de Mus. d'bist. nat. 

 t. vii., iy06. 

 t Grobben, * Die Entwicklungsgeschichte der Moina redtrostris,' p. 56. 



